[deps] Replace Dependabot with Renovate

[ycombinator]

What is the problem this PR solves?

Dependabot can only open Fleet Server dependency update PRs against main. Those updates then need to be backported to every active release branch, where dependency drift often causes conflicts.

Fleet Server recently grouped Dependabot updates in #7517 as a temporary noise-reduction measure while the repository moved to Renovate.

How does this PR solve the problem?

Replaces Dependabot with Renovate, following the Elastic Agent setup from elastic/elastic-agent#15603, elastic/elastic-agent#15837, and elastic/elastic-agent#15873.

The Renovate configuration:

• targets main and all active release branches directly;
• updates the active branch list weekly from the Elastic release schedule;
• discovers all Go modules and retains the existing elastic, test-tooling, and catch-all dependency groups;
• retains weekly GitHub Actions and pre-commit updates;
• enables the dependency dashboard; and
• limits discovery to the explicitly configured managers.

The existing Fleet Server post-dependency workflow is preserved and generalized to support Renovate branches. The Dependabot configuration is removed.

How to test this PR locally

Validate the Renovate configuration:

npx --yes --package renovate@43.285.6 -- renovate-config-validator renovate.json

A local Renovate extraction should discover four Go modules (go.mod, dev-tools/go.mod, pkg/api/go.mod, and testing/go.mod) plus .pre-commit-config.yaml.

Design Checklist

Not applicable: this changes repository dependency automation only and does not affect Fleet Server runtime behavior or scaling.

Checklist

• The Renovate configuration and GitHub workflow YAML files have been validated.
• No documentation or default Fleet Server configuration changes are required.
• No runtime tests are required for this repository automation change.
• No changelog fragment is required; this PR is labeled skip-changelog.

Related issues

• Follows Replace dependabot with renovate elastic-agent#15603
• Follows Fix update-renovate-branches workflow elastic-agent#15837
• Follows Clean up renovate config elastic-agent#15873
• Supersedes the temporary Dependabot grouping from chore: group Go Dependabot updates into a single weekly PR #7517

[mergify]

Tick the box to add this pull request to the merge queue (same as @mergifyio queue).

• Queue this pull request